One of the major considerations when designing ballistic armor of the above kind is its weight. Since armor is meant to be carried by a vehicle or worn by a person, armor having a lower weight is preferred to armor of greater weight which provides the same ballistic protection.
Ballistic armor of the kind to which the present invention refers comprises an armor layer of ceramic tough pellets, adapted to absorb most of the energy of the impacting armor-piercing projectiles. The pellets are typically regularly arranged, and held within a matrix of thermoset or thermoplastic material. Such armor normally has high multi-hit capability, since damage to the armor is localized to one or a small number of pellets at the area of impact. The armor typically further comprises front and/or back layers attached to the armor layer.
U.S. Pat. No. 5,763,813 discloses one example of such armor comprising an armor layer of ceramic pellets and a back layer, and the manufacture of the armor layer by use of a vertical mold. After the armor layer has been produced within the mold, the back layer is attached thereto.
In armor layers of the kind described above, the geometry of the pellets contributes to the ballistic protection capability of the layer. It is appreciated that when pellets have domed ends facing a threat, the impact is better absorbed by the armor layer. Cylindrical pellets having such ends are disclosed, for example, in FR 2559254, EP 699887, DE 3940623, U.S. Pat. No. 5,972,819, and EP 1,522,817. Cylindrical pellets disclosed in these publications have both of their ends domed with the same or different radii of curvature, or only the front end facing the threat being domed. The latter design is disclosed, for example, in U.S. Pat. No. 5,972,819, as an alternative to the former configuration, though it is emphasized that the configuration with both domed ends is most preferred.
EP 1,522,817 discloses a composite armor plate for absorbing and dissipating kinetic energy from high-velocity projectiles. The plate comprises a single layer of pellets which are retained by a binder which may be aluminum, thermoplastic polymers or thermoset plastic, such that the pellets are held in direct contact with each other in a plurality of rows and columns. The pellets are made of ceramic material, and are substantially fully embedded in the binder. Each of the pellets is characterized by a cylindrical body having a first and second end faces, each projecting from the body and having an outwardly decreasing cross-sectional area, wherein the height of the end face disposed substantially opposite to an outer impact receiving major surface of the plate is less than 15% of the length of the diameter of the pellet body from which it projects.